Electric signal for trackless trolley coaches



Nov. 3, 1953 s. s. STOLP 2,658,191

ELECTRIC SIGNAL FOR TRACKLEZSS TROLLEY COACHES Filed July 5, 1951 INVENTOR. 5ANUZ 5. 5 a 1,

A Z'I'OLNE) Patented Nov. 3, 1953 ELECTRIC SIGNAL FOR TRACKLESS TROLLEY COACHES Samuel S. Stolp, Louisville, Ky., assignor to Cheatham Electric Switching Device 00., Incorporated, Louisville, Ky., a corporation of Kentucky Application July 5, 1951, Serial No. 235,155

2 Claims. (Cl. 340--248) This invention relates to an alarm device especially designed for use on coaches operating on a trackless trolley system.

The object of the invention is to devise an arrangement for producing a warning signal in case of a break-down of the insulation between the power circuits and the frame or body of a coach operating on a trackless trolley system. Such a break-down might be dangerous to persons boarding or leaving the coach, or to anyone standing on the ground and touching the coach body.

My charge detector circuit is especially designed for use on coaches provided with rubber tires and operating from a trackless trolley system at a voltage of the order of 600 volts. My charge detector circuit is designed to operate a warning signal if the charge on the coach frame exceeds a value of approximately 50 volts.

A further object is to provide a uni-lateral conducting device, such as a one-way rectifier, in series with the detector circuit to prevent the application of the trolley voltage to the coach frame, through the detector circuit, when the coach is operated temporarily on the wrong side of the street, at which time the collectors are reversed.

My invention is illustrated diagrammatically in the accompanying drawing in which the two trolley wires are shown at l and 2, for supplying current at 600 volts to a coach 3 through the usual collectors 3b and 30 mounted on top of the coach. It will be understood that the coach is provided with rubber tires and the frame of the coach will be insulated from the ground. The negative trolley wire 2 usually is grounded, and in the case of improper insulation between the frame of the coach 3 and any connection leading to the positive trolley wire I the frame will become charged positively with respect to ground. If this positive charge exceeds 50 volts, it may become dangerous to persons using the coach, especially when they are boarding or leaving the coach.

One suitable form of my detector circuit includes a voltage sensitive relay 5 having an operating winding 5a and a switch blade 5b. Relay 5 should operate at low current value, such as one milliampere. The winding 5:; is connected in series with a rectifier 6 in a circuit extending from the frame of the coach to the collector 30 which normally engages negative trolley wire 2. The rectifier 6 shown in the drawing is a doublediode electron tube rectifier having two cathodes 6a and two anodes 61:, but a single-diode may be used if desired. The circuit for relay winding 5 extends from the frame of the coach to the two anode elements of the rectifier 6 through a series resistor l of high resistance value, for example, 30,000 ohms. The cathode of the rectifier is connected to one terminal of the winding 5a and the other terminal of the winding is connected through connection 8 to collector which normally engages the negative trolley wire 2.

The cathode heater 6c of the rectifier 6 is energized by current from the trolley wires through connections, including a series resistor of approximately 8,000 ohms to reduce the voltage applied across the terminals of the heater. The heater circuit also includes a signal lamp l3, preferably of amber color, to indicate that the circuit is in operating condition. This lamp may be shunted by a resistor I2 of approximately 200 ohms to maintain the detector circuit in operation in case the lamp l3 burns out.

Relay 5 is a sensitive relay requiring small current for its operation, and it should operate when the frame of the coach 3 becomes charged to a value of approximately volts with respect to round.

When the relay operates, the blade 52) completes a circuit through a suitable signal device such as one or more signal lamps l4, and an energizing battery I5, to warn the operator that the frame of the coach is charged to a value approaching the danger point. Preferably the signal lamps l4 produce red light to emphasize the dangerous condition.

Sometimes it is necessary to operate the coach temporarily on the wrong side of the street, and in this case the collectors will be reversed so that collector 30 engages the high voltage trolley wire I, while collector 3b engages the grounded wire 2. Under this condition of operation, rectifier 6 will prevent the high voltage of trolley wire I from being applied to the frame of the coach through the detector circuit.

While I have illustrated a preferred form of my detector circuit involving the use of a voltagesensitive relay for controlling the operation of a signal device, it is obviou that other forms of alarm devices may be employed, such as a twoelectrode lamp filled with ionizable gas such as neon. This lamp would be connected in the detector circuit in the place of the relay 5, and the lamp will produce a visible glow when the charge on the coach frame exceeds the ionization voltage of the gas filling.

What I claim is:

1. A charge detector circuit for a two collector coach on a trackless trolley system in which one trolley wire is grounded, said circuit comprising a unilateral conductive device comprising an electron tube having an anode, a cathode, and a heater for the cathode, a high-resistance connection for energizing said heater from the two collectors of said coach, a connection from said anode to the frame of said coach, a resistance element inserted in the connection between the anode and the frame of the coach and having a resistance value of the order of 30,000 ohms, a connection from said cathode to the collector which normally engages the grounded trolley wire, a voltage-sensitive electromagnetic relay having an operating winding included in the last mentioned connec 4 tion, and a signal device controlled by said relay.

2. A charge detector circuit according to claim 1 and including a signal lamp connected in series with the energizing circuit of said cathode heater.

SAMUEL S. STOLP.

References Cited in the file of this patent UNITED STATES PATENTS 

